The present invention refers to an improved process for opening ores, particularly ores containing tantalum, niobium, zirconium and titanium, in which, instead of the usual initial leaching using sulfuric acid (H.sub.2 SO.sub.4) and hydrofluoric acid (HF) for opening ore, the original ore concentrate is initially melted with fluorite (CaF.sub.2), followed by other usual known stages, so that compounds of the desired metals are obtained in much shorter reaction times and without environmental pollutio with hydrofluoric acid as a process effluent.
The usual state of the art processes for opening ores, particularly ores containing Tantalum (Ta), Niobium (Nb), Zirconium (Zr) and Titanium (Ti) include leaching with sulfuric acid and hydrofluoric acid, as described in the following literature: (1) May, S. L., Tews, J. L., and Goff, T. N., "Separation of Tantalum from Columbium by hydrofluoric acid-sulfuric acid-methyl isobuthyl-Ketone System, Report of Investigations 5862 Bureau of Mines U.S.A. 1961; (2) Werning J. R. and Higbie H. B., Tantalum and Niobium separation by liquid-liquid extraction", Industrial and Engineering Chemistry, Vol. 46, No. 12, Dec. 1954, pgs. 2491-2494; and (3) Solvent Extraction Principles and Application, by G. M. Ritey and A. W. Ashbrook, Vol. 2 (1979), pgs. 363-370, Chapter 4.11. In these processes an aqueous solution of mixtures of HF and H.sub.2 SO.sub.4 is prepared containing 20 to 30% of each acid from concentrated acids, after which the ore is slowly added.
The operation is carried out in a stirred reactor which is usually lined with graphite. The addition of ore must be done slowly because of great heat generation (strongly exothermic reaction), which would cause excessive loss of HF.
The purpose of this process step, which is also known as "opening the ore" is to form the following soluble species: H.sub.2 TaF.sub.7 --H.sub.2 NbOF.sub.5 --H.sub.2 TiF.sub.6 --H.sub.2 ZrF.sub.6. Reaction time is approximately 48 hours. After this, free steam is injected into the reaction medium to raise the temperature to approximately 80.degree. C., which helps in the following stage of pulp filtration. The filtrate is then transferred to the liquid-liquid extraction plant and the solid residue is disposed of.
The major drawbacks of these state of the art processes for opening ores containing Ta and Nb are:
(1). Method of operation
The traditional method of acid leaching of ore containing Ta, Nb, Zr, Ti is a batch process which normally is a less efficient operation than a continuous process, and also requires more equipment and greater size thus increasing initial investment considerably.
(2) Reaction time:
A reaction time of 48 hours implies more and larger equipment and thus increases initial investment.
(3) Effluent treatment:
After the Ta and Nb coextraction stage, a large amount of liquid effluent with a high concentration of HF and H.sub.2 SO.sub.4 is generated, requiring elaborate and costly treatment of this effluent prior to disposal.
This prior art method of treatment also uses a large quantity of hydrofluoric acid, whichis an expensive reagent. This further adds to the cost of the process.